The products obtained are suited in themselves to interesting industrial applications as intermediates for organic syntheses, especially as regards the so-called "fine chemicals".
For example, it is possible to obtain, by simple conventional hydrogenation of the double bonds, known acids having wide applicative fields as plasticizers, solvents, additives etc., such as the octanoic acid by hydrogenation of the 3,6- and 2,6-octadienoic acid, suited for plasticizers, fluids for hydraulic brakes, etc.
Furthermore, by utilizing the reactivity of the two double bonds existing in the molecule it is possible to prepare polymers etc.
As far as applicants know, the specific reaction utilized for the process according to this invention for obtaining dienoic acids is not described in the prior art.
According to the art, by means of reactions not pertaining, however, to the one of the present invention, dienoic acids can be actually obtained, through alternative processes based on the Wittig synthesis, starting from aldehydes which are caused to react with organic phosphorous compounds.
Nevertheless, techniques of this type require the preliminary preparation of suitable aldehydes, which are sometimes difficult to be obtained or found, and the stoichiometric use of phosphorous intermediates, which are objectable as regards the compatibility of the effluents with the present environmental requirements, etc. and relevant economic burdens, which render such techniques substantially not practical from an industrial viewpoint.
Finally there are known catalytic processes for the preparation of dienoic acids by reacting unsaturated halides (vinyl, allyl halides) with acetylene and carbon monoxide in hydroxylated solvents in the presence of nickel carbonyl or precursors thereof. These methods are, from an industrial viewpoint, of minor interest for the use of nickel carbonyl derivatives and of carbon monoxide, which are not suitable for industrial applications owing to the high toxicity of the envisaged conditions.
Co-dimerization reactions of alpha-olefins (ethylene) with conjugated dienes (butadiene) in the presence of phosphinic or phosphitic complex catalysts of nickel have been described. Similarly, addition or dimerization reactions of olefins in the presence of rhodium trichloride as a catalyst have been described too; in this way 1,4-diolefins were obtained, for example 1,4-hexadiene from ethylene and butadiene, or dimethyl ester of 2-hexendioic acid from methylacrylate etc.
Nevertheless, such techniques have not proved effective for purposes of obtaining linear products, as experimentally demonstrated in literature, when applied to the co-dimerization reaction of butadiene with alkyls-monosubstituted ethylenes, since such latter ethylenes are attacked on the inner carbon atom of the double bond.
According to the present invention, conversely, in which butadiene and a 3-butenoic acid, also definable as an ethylene monosubstituted by acetic groups, are co-dimerized, the linkage product of butadiene to the outer carbon atom of the acid double bond predominantly forms; prevailingly linear products are obtained.